Aluminum alloy composition, aluminum extrusion tube and fin material with improved corrosion durability comprising same, and heat exchanger constructed of same

ABSTRACT

The present disclosure provides an aluminum alloy with enhanced penetration resistance for a heat exchanger, the alloy containing copper (Cu), and iron (Fe), whose contents are controlled to be equal to or smaller than predetermined contents respectively, and further containing zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof and the remainder being aluminum (Al). Further, the present disclosure provides an aluminum extruded tube and/or an aluminum fin with enhanced penetration resistance made of the alloy respectively. Further, the present disclosure provides a heat exchanger comprising the tube and/or fin. Addition and content-control of the alloy element may spread corrosion initiations and suppress intergranular corrosion to create uniform corrosion. In this manner, the present alloy have superior corrosion resistance compared to pitting corrosion of a previous alloy for a heat exchanger, and, at the same time, have an extrusion rate equal to that of the previous A1070.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims a priority to a Korean patent applicationnumber 2014-0018389 filed on Feb. 18, 2014, which claims a priority to aKorean patent application number 2013-0115043 filed on Sep. 27, 2013,the entire disclosures of which are incorporated herein in its entiretyby reference.

BACKGROUND

1. Technical Field

The present disclosure generally relates to an aluminum alloy withenhanced penetration resistance for a heat exchanger, an aluminum alloyextruded tube and an aluminum alloy fin for a heat exchanger, the tubeand fin being made of the alloy, and a heat exchanger comprising thetube and fin. More particularly, the present disclosure relates to analuminum alloy extruded tube and an aluminum alloy fin for a heatexchanger, and a heat exchanger comprising the tube and fin, where thetube and fin have enhanced penetration and corrosion resistances toprevent the tube and fin from penetration and damage, which otherwiseoccur due to corrosion caused by internal refrigerant and externalcondensed water in the heat exchanger, for example, in anair-conditioner, refrigerator, radiator, etc.

2. Discussion of Related Arts

Recently, a material for a heat exchanger has changed from copper toaluminum in terms of costs, workability, corrosion resistance, etc. Thisis because that aluminum is weight-light, inexpensive, and highlythermal conductive.

Aluminum-based materials for a heat exchanger includes purealuminum-based formulations (A1XXX) with a high extrusion rate, highthermal conductance, and a low cost, and aluminum manganese-basedformulations (A3XXX) with a lower extrusion rate compared to the purealuminum-based formulations, a relatively high strength, and relativelyhigh corrosion resistance.

A following Table 1 describes respective compositions of A1070 and A3003alloys as the previous aluminum-based formulations for a heat exchanger.The A1070 belongs to the pure aluminum-based formulations, while theA3003 belongs to the aluminum manganese-based formulations.

TABLE 1 name Cu Si Fe Zn Mg Mn Ti Al. A1070 0.03 0.20 0.25 0.04 0.030.03 0.03 Remainder A3003 0.158 0.084 0.421 0.034 0.001 1.021 0.014Remainder

The A1070 may be employed for a tube and a fin, for example, in acondenser in home appliances such as an air-conditioner, a refrigerator,etc. where a high strength of the Al based material is not demanded buteconomical aspects such as a low material cost, and a low extrusion costof the Al based material are demanded. To the contrary, the A3003 has ahigher strength and corrosion resistance, but more expensive extrusioncost compared to the A1070, and, thus may be employed for a tube and afin of a heat exchanger in an intercooler, radiator, etc. in anautomobile.

Aluminum may have a high chemical activation, and may form an oxidizedfilm at a surface thereof in an air space to have high corrosionresistance. However, when aluminum undergoes corrosion, there may occura pitting corrosion where corrosion may occur only at a local area inwhich the oxidized film is damaged. Further, the corrosion may propagateand concentrate on a certain area due to electrochemical reaction withvarious impurities in the aluminum alloy. This corrosion mechanism maycause an aluminum heat exchanger to be locally penetrated, leading to aleak of internal refrigerant or hot fluids. Therefore, there is a needfor an aluminum alloy with enhanced penetration resistance for the heatexchanger.

Further, the home appliances have been widely used in China, India etc.suffering from heavy air pollution. In these countries, the aluminumheat exchanger in the home appliances may be susceptible to such a leaktherefrom due to the corrosion. This may be true of a seashore area.This leak may cause economical loss such as a component replacement, andmay lead to deterioration of the home appliances.

FIG. 1 shows a mechanism for pitting corrosion and intergranularcorrosion of a previous aluminum formulation. A left side drawing inFIG. 1 shows a grain-boundary distribution of a cathodic site. To bespecific, a protective passive film is formed on an aluminum surface,and Al₂Cu, Al₃Fe, etc. are distributed along and in the grain boundaryin an intermetallic phase. Upon a start of corrosion, pitting corrosionis initiated, such that, as shown in a middle drawing in FIG. 1, theremay be generated a potential difference between a base material and theintermetallic phase materials Al₂Cu, and Al₃Fe, and, thus, a localcircuit may be created. This may lead to the passive film damage, whichmay confirm the pitting corrosion initiation. Then, as shown in a rightside drawing in FIG. 1, the pitting corrosion propagates. In thisconnection, a propagation rate of the pitting corrosion along the grainboundary may be higher than an initiation rate of new pitting corrosionat the surface of the alloy. This causes a larger penetration depthrelative to an actual corrosion amount. This aluminum corrosionmechanism may cause a local penetration through the aluminum heatexchanger, and, thus, a leak of an internal refrigerant or hot fluidfrom the exchanger.

FIG. 2 illustrates corrosion propagation behavior in a previous aluminumalloy for a heat exchanger. As shown in the figure, a penetration depthbecomes gradually larger due to the propagation of the pitting corrosionas time goes by.

SUMMARY

The present disclosure may provide an aluminum alloy for a tube and afin in a heat exchanger, the alloy having enhanced penetrationresistance and corrosion resistance and, at the same time, a non-loweredextrusion rate, which are not the case in the previous A1070 and A3003aluminum alloys. This may be achieved by adding zirconium (Zr), titanium(Ti), or hafnium (Hf), or a mixture thereof into the alloy and adjustingcomposition ratios thereof to suppress corrosion concentration and thusallow uniform corrosion.

Further, the present disclosure may provide an aluminum alloy extrudedtube and an aluminum alloy fin for a heat exchanger, the tube and finbeing made of the above-defined aluminum alloy, and, thus, havingenhanced penetration resistance. Further, the present disclosure mayprovide a heat exchanger comprising the above-defined tube and fin.

In one aspect of the present disclosure, there is provided an aluminumalloy comprising: copper (Cu); iron (Fe); zirconium (Zr), titanium (Ti),or hafnium (Hf), or a mixture thereof; and the remainder being aluminum(Al), and unavoidable impurities, wherein the zirconium (Zr), titanium(Ti), or hafnium (Hf), or the mixture thereof has a content from 0.05 wt% to 0.2 wt % relative to a total weight of the alloy; wherein contentsof the copper and iron are adjusted such that a PHI (penetration hazardindex) value defined by following equations (1) and (2) is equal to orsmaller than 1.5:

$\begin{matrix}{X = \frac{{0.4 \times {Cu}\mspace{11mu} \%} + {0.5 \times {\exp \left( {{{Fe}\mspace{14mu} \%} - 0.3} \right)}}}{1.24^{({6 \times {Zr}\mspace{14mu} \%})}}} & (1) \\{{PHI} = {{0.1559 \times {\exp \left( {X \div 0.1226} \right)}} - {3.7492\;.}}} & (2)\end{matrix}$

In one embodiment, the alloy may further comprises silicon (Si), whereina content of the silicon may be adjusted to be equal to or smaller than0.2 wt % relative to a total weight of the alloy.

In one embodiment, the alloy may further comprises magnesium (Mg),wherein a content of the magnesium is adjusted to be equal to or smallerthan 0.05 wt % relative to a total weight of the alloy.

In one aspect of the present disclosure, there is provided an aluminumtube with enhanced corrosion resistance for a heat exchanger, the tubebeing made of the above-defined aluminum alloy.

In one aspect of the present disclosure, there is provided an aluminumfin with enhanced corrosion resistance for a heat exchanger, the finbeing made of the above-defined aluminum alloy.

In one aspect of the present disclosure, there is provided a heatexchanger with enhanced corrosion resistance, the exchanger comprisingthe above-defined aluminum tube.

In one aspect of the present disclosure, there is provided a heatexchanger with enhanced corrosion resistance, the exchanger comprisingthe above-defined aluminum fin.

In one aspect of the present disclosure, there is provided a heatexchanger with enhanced corrosion resistance, the exchanger comprisingan aluminum fin and an aluminum tube, wherein both the fin and tube aredefined above.

In accordance with the present disclosure, the above-defined aluminumalloy may have superior penetration resistance and corrosion resistance,compared to the previous A1070 for a heat exchanger, and, thus, havesuperior corrosion and penetration resistances against externalcondensed water and internal refrigerant. To be specific, the additionof the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixturethereof may allow uniform corrosion of the alloy, and, thus, moreenhanced penetration resistance relative to the pitting corrosion.

Furthermore, in accordance with the present disclosure, together withcontrol of contents of the zirconium (Zr), titanium (Ti), or hafnium(Hf), control of contents of the copper (Cu) and iron (Fe) using the PHImay suppress intergranular corrosion, and, thus, may spread corrosionpropagation, leading to enhanced penetration resistance of the alloy.

Furthermore, in accordance with the present disclosure, theabove-defined aluminum alloy may exhibit an extrusion rate (about 90m/min) similar to that of the previous A1070, and, thus, have goodproductivity and economy.

Furthermore, in accordance with the present disclosure, theabove-defined heat exchanger may include components (for example, thefin and tube) thereof with enhanced corrosion resistance, such that theexchanger has a prolonged life span, good performance, and moreenergy-saving effect due to lack of leak of the refrigerant and, thus,improved heat-exchanging efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

A brief description of each drawing is provided to more fully understandthe drawings, which is incorporated in the detailed description of thedisclosure.

FIG. 1 shows a mechanism for pitting corrosion and intergranularcorrosion of a previous aluminum alloy.

FIG. 2 illustrates corrosion propagation behavior in a previous aluminumalloy for a heat exchanger.

FIG. 3A and FIG. 3B illustrate cross-sectional views of a A1070 specimenas a previous 1XXX-based aluminum alloy for a heat exchanger, afterbeing subjected to a potentiostatic polarization test.

FIG. 4A and FIG. 4B illustrate cross-sectional views of a A3003 specimenas a previous 3XXX-based aluminum alloy for a heat exchanger, afterbeing subjected to a potentiostatic polarization test.

FIG. 5 is a schematic view illustrating a pitting corrosion andintergranular corrosion mechanism of an aluminum alloy of the presentdisclosure.

FIG. 6A and FIG. 6B illustrate cross-sectional views of specimens madeof the aluminum alloy in accordance with one embodiment of the presentdisclosure, after being subjected to a potentiostatic polarization test.

FIG. 7 illustrates an aluminum heat exchanger in accordance with oneembodiment of the present disclosure.

FIG. 8 illustrates a graph describing varying PHIs and varying extrusionrates of the present aluminum tube relative to varying zirconiumcontents.

FIG. 9 illustrates a graph describing varying PHIs relative to varyingcopper and iron contents.

FIG. 10 illustrates a graph describing a correlation between an X factorand a PHI value.

DETAILED DESCRIPTIONS

Examples of various embodiments are illustrated in the accompanyingdrawings and described further below. It will be understood that thediscussion herein is not intended to limit the claims to the specificembodiments described. On the contrary, it is intended to coveralternatives, modifications, and equivalents as may be included withinthe spirit and scope of the present disclosure as defined by theappended claims.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a” and “an” are intendedto include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “includes”, and “including” when used in thisspecification, specify the presence of the stated elements, and/orcomponents, but do not preclude the presence or addition of one or moreother elements, components, and/or portions thereof. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Further, all numbers expressing dimensions, physical characteristics,and so forth, used in the specification and claims are to be understoodas being modified in all instances by the term “about”. Accordingly,unless indicated to the contrary, the numerical values set forth in thefollowing specification and claims can vary depending upon the desiredproperties sought to be obtained by the practice of the presentdisclosure. Moreover, all ranges disclosed herein are to be understoodto encompass any and all subranges subsumed therein. For example, astated range of “1 to 10” should be considered to include any and allsubranges between (and inclusive of) the minimum value of 1 and themaximum value of 10; that is, all subranges beginning with a minimumvalue of 1 or more and ending with a maximum value of 10 or less, e.g.,1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent disclosure refers to “one or more embodiments of the presentdisclosure.”

In one embodiment of the present disclosure, an aluminum alloy withenhanced penetration resistance includes copper (Cu); iron (Si);zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixture thereof;the remainder being aluminum (Al), and unavoidable impurities.

Hereinafter, a reason for content control of each component, and aproperty thereof will be first described, which, in turn, will besupported by a numerical-limitation example using experiment data for anumerical content of each component.

In one embodiment of the present disclosure, the aluminum alloy withenhanced penetration resistance contains zirconium (Zr), titanium (Ti),or hafnium (Hf), or a mixture thereof. The zirconium (Zr), titanium(Ti), or hafnium (Hf), or a mixture thereof may not only refine a grainsize to improve strength of the alloy, but also suppress pittingcorrosion and, thus, allow uniform corrosion. The suppression of pittingcorrosion, and, thus, creation of the uniform corrosion may be achievedas follows: the addition of the zirconium (Zr), titanium (Ti), orhafnium (Hf), or a mixture thereof may generate a potential differencein the alloy to finely spread precipitations serving as initiationpoints for corrosion, and thus, may suppress the pitting corrosionoccurring locally and intensely and thus hard to predict corrosionlocations. To achieve the uniform corrosion, respective optimal contentsof the above components may be determined from a following Table 2.

TABLE 2 corrosion corrosion depth depth standard extrusion Cu Fe Zr Alaverage (μm) deviation PHI rate (m/min) 1 0.21 0.42 0.001 Remainder175.59 154.7 27.171 90 2 0.19 0.38 0.06 Remainder 171.81 57.63 9.9021 903 0.22 0.4 0.13 Remainder 127.25 53.53 6.8121 90 4 0.19 0.39 0.21Remainder 103.31 31.03 3.2058 84 5 0.20 0.41 0.41 Remainder 98.21 24.672.4225 32

In the above Table 2, a content of each component refers to a content in% by weight. In order to determine an optimal zirconium content,experiment conditions are set such that a content of zirconium isvariable, while each of contents of copper, and iron is controlled to agiven content. As shown from the Table 2, the results of the experimentsindicate corrosion depth averages and corresponding corrosion depthstandard deviations, and PHIs and extrusion rates, depending on thevarying contents of the zirconium. In this connection, based on theTable 2, the PHIs and extrusion rates depending on the varying contentsof the zirconium are graphically presented as shown in FIG. 8.

As used herein, a PHI refers to an acronym of a “penetration hazardindex”. The PHI may be calculated by means of a corrosion penetrationdepth of an aluminum tube after being subjected to electrochemicalcorrosion acceleration. Thus, The PHI may serve as a measure ofcorrosion resistance of an aluminum alloy. A lower PHI value may meansuperior corrosion resistance of an aluminum alloy.

The PHI may be expressed as follows:

PHI=(corrosion depth average)×(corrosion depth standard deviation)/1000.

In order to calculate the PHI, an aluminum alloy specimen is subjectedto electrochemical corrosion acceleration in a synthetic acid rain, and,then, a cross-section of the resulting specimen is analyzed to measure acorrosion depth average and a corrosion depth standard deviation.

As seen from the above Table 2, in terms of the PHI and extrusion rate,an optimal Zr content may be 0.05 wt % to 0.2 wt %. This is due tofollowing facts: an alloy composition of No. 1 in the Table 2 (whose Zrcontent is smaller than 0.05 wt %) may not suppress a crack in the alloydue to a much smaller Zr amount (this is confirmed from a remarkablyhigh PHI value), while alloy compositions of No. 4 and No. 5 in theTable 2 (whose Zr content is larger than 0.2 wt %) may lower anextrusion rate of the alloy due to a much larger Zr amount. In thisconnection, in the present disclosure, it is desirable that the aluminumalloy should not only exhibit uniform corrosion, but also maintain anextrusion rate.

When the zirconium (Zr), titanium (Ti), or hafnium (Hf), or a mixturethereof is added to the aluminum alloy, an intergranular corrosionmechanism of the alloy may be as follows:

FIG. 5 is a schematic view illustrating a pitting corrosion andintergranular corrosion mechanism of the present aluminum alloy. Asshown in FIG. 5, in the aluminum alloy in accordance with the presentdisclosure, the addition of the zirconium (Zr), titanium (Ti), orhafnium (Hf), or a mixture thereof may allow a decrease of a residenceof Al₂Cu, Al₃Fe, etc. in the grain boundary in the intermetallic phase,and, thus, spread the residence of Al₂Cu, Al₃Fe, etc. For a comparison,in FIG. 1, the Al₂Cu, Al₃Fe, etc. mainly reside in the grain boundary,while in FIG. 5 (see a left side drawing therein), the residence of theAl₂Cu, Al₃Fe, etc. in the grain boundary may decrease.

Further, as shown in a middle drawing of FIG. 5, it is confirmed thatupon start of pitting corrosion, corrosion initiation points aredisperse. For a comparison, in FIG. 1, upon start of pitting corrosion,the corrosion occurs in a local and concentrated manner.

Finally, as shown in a right drawing of FIG. 5, it is confirmed thatupon propagation of the pitting corrosion, the corrosion may notconcentrate on a certain location, and, thus, may be suppressed in adeep and inwardly direction. As a result, upon the pitting corrosionpropagation, inwardly penetration may be less probable. To the contrary,in FIG. 1 (see a right side drawing therein), the pitting corrosion maypropagate along the grain boundary, and, thus, the inwardly penetrationdepth may be larger than that in the aluminum alloy of the presentdisclosure.

Next, an experiment for measuring the PHI values, and the PHI valuesdepending on aluminum alloy compositions may be as follows:

In order to calculate the PHI, an aluminum alloy specimen is subjectedto electrochemical corrosion acceleration in a synthetic acid rain, and,then, a cross-section of the resulting specimen is analyzed to measure acorrosion depth average and a corrosion depth standard deviation.Details about an experimental procedure are as follows: first, a surfaceof the aluminum alloy specimen is polished using a #600 SiC paper, and,then, an exposure area thereof is controlled to be 1 cm×1 cm. Then, thespecimen is immersed for 4 hours in a test solution (synthetic acidrain) of pH 5 containing 4 ppm SO4²⁻, 1.5 ppm NO²⁻, and 2 ppm Cl⁻ tostabilize a surface state of the specimen. Thereafter, the specimen hasa constant potential of 0.25 V applied thereto for 6 hours, thepotential being relative to SCE (saturated calomel electrode), toaccelerate corrosion in a constant rate. The synthetic acid rainsimulates a corrosion environment to which a heat exchanger including analuminum tube is exposed in an air space. The electrochemicalacceleration method simulates a corrosion mechanism identical with anactual corrosion environment purely in an electrochemical manner. Theelectrochemical acceleration method may be more similar to the actualcorrosion environment than an existing chemical acceleration method.Further, in the electrochemical acceleration method, since the sameacceleration energy is applied to all specimens, differences incorrosion resistances between the specimens may be evaluated in a morereliable manner. A following Table 3 indicates chemical compositions,corrosion penetration depths after the electrochemical acceleration, andthe PHI values for 11 aluminum specimens. In the Table 3, a No. 11specimen is made in accordance with one embodiment of the presentdisclosure. As seen from the Table 3, when a PHI value is smaller thanor equal to 1.5, corrosion resistance of the alloy is superior. Fromcomparison of the PHI values between previous alloys (No. 1 to No. 10specimens) and the present alloy (No. 11 specimen), it is confirmed thatwhen the PHI value of the alloy is smaller than or equal to 1.5, thealloy exhibits a relatively low average corrosion depth and standarddeviation, which means that corrosion of the alloy occurs and propagatessubstantially uniformly, and, thus, the alloy has sufficient corrosionresistance enhancement.

Corrosion Corrosion penetration penetration depth depth average standardCu Fe Zr Al (μm) deviation PHI 1 0.006 0.098 0 Remainder 64.74 28.011.813 2 0.003 0.246 0 Remainder 75.29 65.84 4.957 3 0.005 0.46 0Remainder 156.81 92.56 14.514 4 0.158 0.421 0 Remainder 190.97 150.3128.705 5 0.2 0.51 0 Remainder 265.59 143.72 38.171 6 0.5 0.07 0Remainder 236.97 65.22 15.455 7 0.21 0.42 0.001 Remainder 175.59 154.727.171 8 0.19 0.38 0.06 Remainder 171.81 57.63 9.9021 9 0.22 0.4 0.13Remainder 127.25 53.53 6.8121 10 0.19 0.39 0.21 Remainder 103.31 31.033.2058 11(present 0.005 0.2 0.1 Remainder 40.68 14.41 0.586 alloy)

As seen from the Table 3, when the present alloy (No. 11 specimen) hasthe PHI value smaller than or equal to 1.5, and, thus, exhibits arelatively low average corrosion depth and standard deviation, whichmeans that corrosion of the alloy occurs and propagates substantiallyuniformly. Although the previous alloy (No. 1 specimen) has a low PHIvalue, contents of the copper and iron may not be adjusted to low levelsas in the No. 1 specimen due to technical difficulty and economicalaspects.

Hereinafter, descriptions will be made about controls of contents of thecopper and iron in connection with the above-described PHI value and theoptimal content of the zirconium.

Regarding an alloy formation, when a metal has a different elementinjected intentionally thereto, the element is referred to as an alloyelement. Meanwhile, impurities are unavoidably injected into the alloydue to a technical limitation and an economical aspect during the alloyformation. The impurities may be limited in contents thereof by contentsequal to or smaller than acceptable amounts, and, thus, presencesthereof in the alloy may be acceptable. The acceptable contents of theimpurities may depend on what extent of harm the impurities give themetal.

Specifically, the copper (Cu) may react with the aluminum and hence beprecipitated into Al₂Cu promoting the cathodic reaction of corrosion.The copper may mainly reside in a continuous or networking manner alongthe grain boundary of the aluminum, and, thus, may be a factor forintergranular corrosion where the corrosion damage propagates along thegrain boundary. This intergranular corrosion may cause the aluminumalloy for a heat exchanger to be susceptible to the penetration. Inorder to avoid the intergranular corrosion, the copper should becontrolled in a content thereof by a content smaller than a high contentat a room temperature.

The iron (Fe) may react with the aluminum and silicon to generateprecipitations acting as initiation points of cathodic reactions incorrosion environment, thereby to play a considerable role for thealuminum corrosion. Thus, the iron content should be minimized. However,the precipitations derived from the irons may reside in a non-continuousor isolated manner and, thus, be less susceptible to the interganularcorrosion compared to the copper. Further, in order to reduce thecontent of the iron below a low concentration, a high cost may occur.Therefore, the iron (Fe) content should be controlled fromconsiderations of the above.

The copper and iron may play a significant role in aluminum corrosion ina corrosion environment based on a content correlation between there.Thus, in the present disclosure, the content correlation is determinedto suppress intergranular corrosion.

Not only the zirconium (Zr), titanium (Ti), or hafnium (Hf), or amixture thereof, but also the copper (Cu) and iron (Fe) may affect theintergranular corrosion. FIG. 9 illustrates a graph describing varyingPHIs relative to varying copper and iron contents. It is confirmed thatwhen a content of copper is equal to or larger than 0.01 wt %, theintergranular corrosion may occur, and, thus, the PHI may increase. Whena content of copper is equal to or larger than 0.01 wt %, the copper mayprecipitate along the grain boundary of the aluminum in a continuous ornetworking manner. This continuous or networking manner of theprecipitation may allow the corrosion of the aluminum alloy, forexample, an aluminum tube to propagate along the grain boundary and,thus, be susceptible to penetration. Therefore, it is observed that whena content of copper is equal to or larger than 0.01 wt %, the content ofthe copper and the PHI have a linear correlation. Meanwhile, it isconfirmed that when a content of iron is equal to or larger than 0.2 wt%, the PHI may increase exponentially. The iron may act as a highlycorrosive impurity. However, the iron may be individually spread in aform of islands in the aluminum in a low concentration thereof, and,thus, may not cause intergranular corrosion. This is not true of thecopper. When the iron content increases, precipitations thereof whichare individually spread in the low concentration of the iron mayincrease and thus form a continuous form thereof to allow the corrosionto occur in a continuous manner as in the intergranular corrosion. Inthis way, it is confirmed that when a content of iron is equal to orlarger than 0.2 wt %, the PHI may increase exponentially. From theconsiderations of the above facts, a relationship between the contentsof the iron and copper and the PHI value is that a sum of the contentsof the copper and iron equal to or larger than critical amountsrespectively may increase the PHI value. In addition to this, asindicated in the Table 2, the zirconium content may also affect theintergranular corrosion (the larger the Zr content is, the lower the PHIis; the optimal Zr content may be 0.05 to 0.2 wt %). Thus, the zirconiumcontent should be taken into account.

From comprehensive considerations of the above facts, the PHI may beexpressed as follows:

$\begin{matrix}{{{PHI} = {f(X)}};{where}} & \; \\{{X = \frac{{0.4 \times {Cu}\mspace{11mu} \%} + {0.5 \times {\exp \left( {{{Fe}\mspace{14mu} \%} - 0.3} \right)}}}{1.24^{({6 \times {Zr}\mspace{14mu} \%})}}};} & (1)\end{matrix}$

where the X factor refers to concentrations of alloy elements. That is,the PHI may be expressed as a function of the X factor.

In this connection, FIG. 10 illustrates a graph describing a correlationbetween the X factor and the PHI value. It may be seen from this graphthat the X factor and the PHI value have an exponential relationship,which may be expressed as follows:

PHI=0.1559×exp(X÷0.1226)−3.7492  (2).

When the PHI is adjusted to be equal to or smaller than 1.5 (asaddressed above) based on the above equations (1) and (2), and the Zrcontent is adjusted to be 0.05 to 0.2 wt % (as addressed above), arelationship about the Cu and Fe contents is as follows:

Although the PHI value may be adjusted to be equal to or smaller than1.5, the PHI value is fixed to 1.5 for the sake of an exemplarysimplified calculation. In this connection, the PHI 1.5 may suffice tosuppress the intergranular corrosion and thus obtain enhanced corrosionresistance of the aluminum alloy for a fin and a tube of a heatexchanger. Of course, the PHI value smaller than 1.5 may be morepreferable. The PHI value 1.5 may be employed to define a maximumnumerical range.

Based on the equation (2), when the PHI is 1.5, X is 0.4311. In thiscase, the Zr content of 0.05 to 0.2 wt % is applied to the equation (1).The result is as follows:

0.4598≦0.4×Cu %+0.5×exp(Fe %−0.3)≦0.5580  (3).

In this connection, since the lowest contents of the copper and iron maybe ideal, a minimum value, that is, the left side value in the equation(3) is not meaningful, and, thus is ignored. In addition to, the rightside value is rounded off. Hence, a final relationship about the Cu andFe contents is as follows:

0.4×Cu %+0.5×exp(Fe %−0.3)≦0.56  (4).

Therefore, in order to suppress intergraular corrosion, the Cu and Fecontents may be adjusted as in the equation (4).

The aluminum alloy composition of one embodiment of the presentdisclosure may contain silicon and magnesium impurities beside thecopper and iron. Thus, the silicon and magnesium impurities should belimited in contents thereof as follows.

The magnesium (Mg) may react with the silicon (Si) to formprecipitations to improve alloy strength. However, the magnesium (Mg)may create an oxide film to deteriorate brazing bonding ability. Thus,the Mg content should be minimized. In the present disclosure, the Mgcontent may be controlled to be as follows: 0 wt %<Mg≦0.05 wt %. Whenthe Mg content exceeds 0.05 wt %, the brazing bonding ability may bedeteriorated, leading to poor brazing process. Thus, the Mg contentshould be adjusted to be equal to or smaller than 0.05 wt %. Further,because of an economical aspect, the alloy may avoidably contain theimpurity Mg, and, thus, the Mg content has no choice but to exceed zero%.

The silicon (Si) may react with unavoidable impurities (magnesium) togenerate precipitations, which may promote cathodic reaction incorrosion environment. Thus, the silicon content should be minimized. Inthe present disclosure, the silicon (Si) content may be controlled to begreater than 0% by weight and equal to or smaller than about 0.2% byweight.

Although, in order to reduce the corrosion, it is preferable thatcontents of the above-mentioned impurities, namely, copper, iron,silicon and magnesium should be minimized, the contents thereof may becontrolled to the above-defined contents due to the economical aspect.The above-defined contents thereof may suffice to provide the goodaluminum alloy for a heat exchanger as illustrated below.

FIG. 3A and FIG. 3B illustrate cross-sectional views of a A1070 specimenas a previous 1XXX-based aluminum alloy for a heat exchanger, afterbeing subjected to a potentiostatic polarization test. FIG. 4A and FIG.4B illustrate cross-sectional views of a A3003 specimen as a previous3XXX-based aluminum alloy for a heat exchanger, after being subjected toa potentiostatic polarization test. FIG. 6A and FIG. 6B illustratecross-sectional views of specimens made of the aluminum alloy inaccordance with one embodiment of the present disclosure, after beingsubjected to a potentiostatic polarization test.

In the potentiostatic polarization test, a constant voltage is appliedand maintained to the specimen to accelerate corrosion. This test may beuseful to evaluate a corrosion resistance of the alloy. In the presentdisclosure, the alloy specimen is subjected to the potentiostaticpolarization test for 6 hours using the synthetic acid rain simulatingthe external condensed water, and a cross-section of the resultingspecimen is measured in terms of a corrosion depth.

Referring to FIG. 3A, FIG. 3B, FIG. 4A, FIG. 4B, FIG. 6A and FIG. 6B, acomparison between the present and previous alloys will be made in termsof the penetration depth. In this comparison, the penetration depth maybe relative to the reference line (red line). In case of previous A1070and A3003 specimens, corrosion is concentrated on a certain region, andpropagate inwardly along the grain boundary, to form a large penetrationdepth. To the contrary, in case of the present specimen, corrosion isspread along the reference line, that is, a surface line of the alloy,and an intergranular corrosion may not occur and, thus, create a uniformcorrosion, to form a small penetration depth. Hence, it is confirmedthat the present specimen has a greater decrease in the corrosionpropagation than in the A1070 and A3003 specimens.

The following Table 4 indicates corrosion depth measurements of theprevious A1070 and A3003 specimens, and the present specimens made ofthe aluminum alloy of one embodiment of the present disclosure, afterbeing subjected to the potentiostatic polarization test.

TABLE 4 Corrosion depth (thinning) (μm) A1070 A3003 Present alloy 1236.03 184.25 41.56 2 262.82 58.41 30.86 3 240.00 97.25 28.34 4 37.4749.51 39.06 5 245.58 48.54 30.86 6 57.48 124.31 34.01 7 98.27 88.4151.64 8 42.62 157.52 62.97 9 23.78 121.24 23.30 10 147.32 35.45 64.24Average 139.14 96.49 40.68 Standard deviation 98.63 50.07 14.40

Referring to the Table 4, the A1070 specimens exhibit an averagecorrosion depth of 139.14 μm, and a standard deviation of 98.63 μm. TheA3003 specimens exhibit an average corrosion depth of 94.49 μm, and astandard deviation of 50.07 μm. To the contrary, the present specimensmade of the aluminum alloy of one embodiment of the present disclosureexhibit an average corrosion depth of 40.68 μm, and a standard deviationof 14.4 μm. In other words, the present specimens made of the aluminumalloy of one embodiment of the present disclosure exhibit about 3.5times corrosion resistance improvement compared to the A1070 specimens.Further, the present specimens made of the aluminum alloy of oneembodiment of the present disclosure exhibit an overall loweredcorrosion depth deviation which means that a uniform corrosion occurs,leading to enhanced penetration resistance.

Furthermore, the present specimens made of the aluminum alloy of oneembodiment of the present disclosure exhibit a good extrusion rate ofabout 90 m/min. This rate may be substantially equal to an extrusionrate of the previous A1070, and may be higher than an extrusion rate ofthe previous A3003 which is about 60-70 m/min. That is, the presentspecimens made of the aluminum alloy of one embodiment of the presentdisclosure may have a superior extrusion rate compared to the previousA3003.

The aluminum alloy of one embodiment of the present disclosure may beemployed for not only an extruded tube but also for a fin in a heatexchanger.

FIG. 7 illustrates an aluminum heat exchanger in accordance with oneembodiment of the present disclosure. The heat exchanger comprisingthose extruded tube and fin may be classified into a stack type, a tubetype, draw-on cap type, etc. in terms of a structure.

In particular, the tube type heat exchanger may increase heatdissipation via a fin internally attached thereto or a pipe havingmultiple holes formed therein. Specifically, the heat exchanger may bemanufactured by provisionally assembling the extruded tube with a fin, aplate and a side tank, etc. and fixing one another via a clamp, andapplying a flux treatment to the fixed structure, and passing thestructure through a brazing furnace.

In this way, the aluminum alloy of the present disclosure for the heatexchanger has greatly enhanced corrosion resistance, and, thus, the heatexchanger made of the alloy has enhanced penetration resistance, leadingto a prolonged life span and improved performance.

The above description is not to be taken in a limiting sense, but ismade merely for the purpose of describing the general principles ofexemplary embodiments, and many additional embodiments of thisdisclosure are possible. It is understood that no limitation of thescope of the disclosure is thereby intended. The scope of the disclosureshould be determined with reference to the Claims. Reference throughoutthis specification to “one embodiment,” “an embodiment,” or similarlanguage means that a particular feature, structure, or characteristicthat is described in connection with the embodiment is included in atleast one embodiment of the present disclosure. Thus, appearances of thephrases “in one embodiment,” “in an embodiment,” and similar languagethroughout this specification may, but do not necessarily, all refer tothe same embodiment.

1. An aluminum alloy comprising: copper (Cu); iron (Fe); zirconium (Zr);and the remainder being aluminum (Al), and unavoidable impurities,wherein the zirconium (Zr) comprises a content from 0.05 wt % to 0.2 wt% relative to a total weight of the alloy, and contents of the copperand iron are adjusted such that a PHI (penetration hazard index) valueis equal to or smaller than 1.5, in accordance with equations (1) and(2), in which:X=0.4×Cu %+0.5×exp(Fe %−0.3)/1.24^((×Zr %))  (1)PHI=0.1559×exp(X÷0.1226)−3.7492  (2).
 2. The alloy of claim 1, furthercomprising silicon (Si), wherein a content of the silicon is adjusted tobe equal to or smaller than 0.2 wt % relative to a total weight of thealloy.
 3. The alloy of claim 1, further comprising magnesium (Mg),wherein a content of the magnesium is adjusted to be equal to or smallerthan 0.05 wt % relative to a total weight of the alloy.
 4. The alloy ofclaim 2, further comprising magnesium (Mg), wherein a content of themagnesium is adjusted to be equal to or smaller than 0.05 wt % relativeto a total weight of the alloy.
 5. An aluminum tube with enhancedcorrosion resistance for a heat exchanger, the tube being made of thealuminum alloy of claim
 1. 6. An aluminum fin with enhanced corrosionresistance for a heat exchanger, the fin being made of the aluminumalloy of claim
 1. 7. A heat exchanger with enhanced corrosionresistance, the exchanger comprising an aluminum tube and an aluminumfin, the tube and fin both being made of the alloy of claim 1.